Also, on ancestry.com, there are periods of time where they will make certain records free: military records on Veterans Day, Civil War records one April (150th anniversary?), etc. If you allow them to send you emails, you'll be notified when they do something like this. It's usually a weekend or maybe a week where certain records are free. Once you find them, you can attach them to a person in your tree, but when the free period is over, you won't be able to access that record anymore, even if it's attached to someone in your tree (well, until you pay for a subscription, I suppose). So, be sure to download a copy to your computer if possible, or copy/paste into a word document. That way, you won't lose what you found!
I found a Civil War record that showed when and where a relative was captured and imprisoned, and subsequently it showed when he was released (after the war had officially ended)... something like "upon oath of loyalty." I'd have to look at the document again for the exact wording, but basically he was a Confederate soldier who had to take an oath of allegience to the Union once he was released, even after the fighting had stopped. Very interesting!